1. Field of the Invention
The present invention relates generally to systems and methods for monitoring signal qualities of a transmitted signal based on measuring the received signal, and particularly for measuring carrier, interference and noise power in a satellite signal.
2. Description of the Related Art
In systems employing transmitted signals it is often necessary to estimate the signal quality to obtain an indication of the system performance. There is also a need to monitor frequency reuse across a multiple coverage areas. For example, satellite systems employing spotbeams with substantially similar transmission frequencies over adjacent coverage areas may interfere at their boundaries. It is important to be able to accurately identify the signal quality at these boundaries to optimize the overall signal patterns. Carrier, interference and noise power levels are examples of important signal qualities that may be measured. Carrier power indicates the strength of the signal and hence, where it may be received by a receiver. Noise and interference, however, may distort a received signal and prevent its use even if the carrier power is otherwise sufficient. Thus, the carrier to noise ratio (CNR) and the carrier to interference ratio (CIR) are two significant measures of signal quality. The interference to noise ratio (INR) is another property of interest, which may be derived from CNR and CIR.
The CIR of a transmitted signal has been estimated by analyzing a link budget with propagation and geometric parameters, such as the relative transmitter power, position and range, and antenna look angle and pattern. Several methods have been used this way to estimate the CNR, ranging in accuracy and complexity. Systems and methods which accurately measure signal qualities (including CIR and CNR) employing a systematic and unified methodology would be very useful. Such systems and methods may be used to optimize the power control for any given transmitted signal.
In addition, systems which may employ overlapping beams with substantially similar transmission frequencies are improved with signal quality feedback to optimize their operation. Communication systems which employ layered modulation, such as described in co-pending and commonly assigned application Ser. No. 09/844,401, filed Apr. 27, 2001, by Ernest Chen and entitled “LAYERED MODULATION FOR DIGITAL SIGNALS”, which is hereby incorporated by reference herein, are examples of such systems.